INSECTS. 



231 



have 25,000. If examined with a microscope, the sur- 

 face of these compound eyes appears as you see in Fig. 

 181 (p. 230), representing the head and eyes of a bee. 

 At a are the antenna, and the eyes occupy most of the 

 front and sides of the head. The surface is made up of 

 hexagonal (six-sided) facets. At A you see them much 

 magnified, and at B you see hairs standing out between 

 them. Each of these facets is a cornea, or window to a 

 little eye. (See "First Book in Physiology," p. 167.) 

 Most insects have these compound eyes, but some have 

 only single ones, and some have both, for what reason 

 we do not know. 



396. The digestive apparatus is commonly quite com- 

 plicated, there being three 

 stomachs one correspond- 

 ing to the crop of birds, an- 

 other to the gizzard, while a 

 third receives the food and 

 digests it after it has been 

 softened and ground in the 

 other two stomachs. The 

 second stomach, or gizzard, 

 is often armed with horny 

 projections, in order to grind 

 up the food effectually. In 

 Fig. 182 you have the whole 

 digestive apparatus of a 

 Beetle. First you see the 

 strong cutting mandibles, 

 the maxillaB and the anten- 

 na3 ; then a the throat, b the 

 gullet, c the crop, d the giz- 

 zard, e the third stomach, 

 /"the intestine. The liver, A, 

 instead of being such a solid 

 organ as it is in vertebrate 



A'ig. 182. Digestive Apparatus of 



Beetle. and most other animals, is 



